The present invention relates to a data storage tape cartridge. More particularly, it relates to a data storage tape cartridge having an exposed datum for improved tape registration.
Data storage tape cartridges have been used for decades in the computer, audio and video fields. While other forms of media storage, such as disk cartridges, are also available, the data storage tape cartridge continues to be an extremely popular form of recording large volumes of information for subsequent retrieval and use.
The data storage tape cartridge generally consists of an outer shell or housing maintaining at least one tape reel and a length of magnetic storage tape. The storage tape is wrapped about a hub portion of the tape reel and is driven through a defined tape path by a driving system. The housing normally includes a separate cover and base, the combination of which creates an opening (or window) of some type for allowing access to the storage tape by a read/write head upon insertion of the data storage tape cartridge into a tape drive. This interaction between storage tape and head may take place within the housing (e.g., a mid tape load design), or the storage tape may be directed away from the housing to an adjacent area at which the read/write head is located (e.g., a helical drive or a leader block design). Location of the storage tape within the housing is of minimal concern where the data storage tape cartridge is configured to have the storage tape directed from the housing to a separate head location. Conversely, where the tape cartridge/drive system is designed to provide head-storage tape interface within or very near the housing, precise positioning of the storage tape adjacent the window is extremely important. In this regard, positioning of the storage tape is dictated exclusively by the tape path defined within the tape cartridge housing.
In particular, with the internalized head-storage tape interface approach, the data storage tape cartridge normally includes two tape reels. The tape path is defined by the location of the tape reels maintaining the storage tape, as well as by various tape guides positioned within the housing. The tape reels are normally rotatably associated with either the cover or the base, and each includes a hub and opposing radial flanges. The storage tape is wrapped around the hub, between the opposing radial flanges. Generally speaking, then, with a two-tape reel design, the storage tape extends between the two hubs, along the tape guides. The tape guides are strategically positioned within the housing such that at the cartridge window, the storage tape is approximately parallel to a plane of the window.
Recent advancements in tape drives, read/write heads and magnetic tape media have greatly enhanced performance capabilities of the data storage tape cartridge. For example, evolution of magnetic tape media has resulted in storage tapes with increased storage capacity and product longevity. In the same regard, present day read/write heads are able to read and record information on increasingly smaller data tracks defined across a height of the storage tape. By employing reduced-size data tracks, the volume of information stored on the storage tape increases dramatically.
The improvements in read/write heads and magnetic tape media have placed greater demands on the data storage tape cartridge design. For example, in order for the read/write head to consistently interact with the storage tape at each of the tracks, the storage tape must be precisely positioned at the cartridge window. Any slight deviation from the desired planar positioning of the storage tape at the cartridge window may result in errors. If the storage tape is slightly above or below an expected location, upon insertion into the tape drive the read/write head will experience difficulties in finding a desired track. Similar problems occur if the tape path generates an angular orientation of the storage tape across the cartridge window. Obviously, the potential for read/write errors becomes more prevalent where reduced-size tracks are utilized.
Data storage tape cartridge designers have sought to address the above-described tape path positioning concern by, for example, positioning tape guides at opposite sides of the cartridge window. The tape guides serve to guide or position the storage tape across the cartridge window at a desired level and in a desired plane. In theory, then, when the data storage tape cartridge is inserted into the tape drive, the read/write head will engage the storage tape at this controlled position. Unfortunately, however, tape guides alone may be insufficient for locating the storage tape within the tight tolerances required by use of reduced-size data tracks.
For example, the tape guides and tape reels are commonly secured to an interior surface of either the base or the cover, both of which are normally molded plastic. While every effort is made to manufacture the base and/or cover as flat as possible, deformities are likely to occur. Similarly, over time, the plastic material may warp or otherwise bend. In either instance, the level (or height) of the various components maintained within the housing will change, either individually or as a whole. Even a minor change in the height of a single tape guide can alter the tape path to a point where reading/writing errors occur. More recently, the plastic cover has been replaced with a metal plate to which the tape reels and tape guides are attached. While use of a metal plate, at least initially, eliminates the inherent deformities associated with plastic molding, over time the metal plate can become damaged. Because an entire face of the metal plate is completely exposed, with repeated use, the metal plate will bend, dent, etc., again resulting in potentially catastrophic tape path deviation.
Even if the various components are attached to the cover (plastic or metal) or base at a precise height, registration problems within the tape drive may still occur. The tape drive normally includes a loader having a registration device. The loader initially receives and directs the data storage tape cartridge within the tape drive. The registration device then aligns the data storage tape cartridge adjacent the read/write head. Even a slight error in locating the data storage tape cartridge within the tape drive may result in the same read/write errors described above. Simply stated, proper registration of the data storage tape cartridge within the tape drive is equally as important as defining a consistent tape path within the cartridge housing itself.
One typical loader/registration device includes a slot in a frame of the tape drive sized to receive the cartridge housing. The data storage tape cartridge is thus inserted along the slot into the tape drive, with the slot having a known position and relationship with respect to the read/write head. Additionally, a suspension system of some type may be provided for supporting the cartridge housing at a certain location. Unfortunately, this generally accepted approach of locating the data storage tape cartridge within the tape drive may not provide consistent registration of the storage tape with the head. The above-described registration device relies solely upon the cartridge housing for alignment within the tape drive. Once again, the cartridge housing is normally made of a molded plastic material. Surface irregularities inherently resulting from plastic molding processing create unavoidable deviations in the flatness of the housing. In other words, even when the various internal components are properly secured to an interior surface of the housing, incorrect registration may occur where the exterior surface fluctuates even slightly. Further, where the internal components are secured to the cover, for example, and registration within the tape drive is made with reference to the base, inaccurate registration may occur. Additionally, because the cartridge housing may warp or bend over time, registration within the tape drive may change from use to use. Under these circumstances, it is quite possible that the read/write head will be unable to locate a track onto which information was previously recorded. In short, use of the plastic cartridge housing as a point of reference for registering the storage tape relative to the read/write head may lead to errors due to material irregularities, tolerance build-ups, positioning of the storage tape within the housing, etc.
Data storage tape cartridges are important tools used to maintain vast amounts of information. However, with increasingly complex reading/writing and magnetic tape technology, design of the data storage tape cartridge must evolve to provide accurate storage tape positioning and registration within tight tolerances. Therefore, a need exists for a data storage tape cartridge providing improved registration within a tape drive.